Multi-channel electron multipliers, now often called micro-channel plates ("MCP"'s), are well known in the art; so are pairs of such devices arranged with their channels oriented in directions not parallel; such a device is disclosed in Goodrich U.S. Pat. No. 3,373,380, "Apparatus for Suppression of Ion Feedback in Electron Multipliers", issued Mar. 19, 1968. Also, it has been known for some years to flare the inlets of the downstream plate channels, as done in the preferred embodiment disclosed hereinbelow. It has been known also to use the output of an MCP to produce a trace ("write") on a phosphor screen.